1. Field of the Invention
The present invention relates to a semiconductor device and to a method for manufacturing a semiconductor device, and more particularly it relates to a compact, thin semiconductor device, and to a method of manufacturing a semiconductor device with high productivity.
2. Background of the Invention
In recent years, in response to the demand for electronic equipment with sophisticated functions, compactness, lightweight, and high speed, a variety of forms of semiconductor devices are being developed. For example, this is not even limited to integrated circuits, there being a demand for compactness and light weight in such discrete components as diodes and transistors as well.
For example, in a transistor of the past, there has been a configuration in which electrodes for outputting signals have been provided on a main surface and other electrodes have been provided on a surface that is opposite the main surface of the chip 1. In contrast to this approach, in response to recent demand for compactness in semiconductor devices, there have been attempts to achieve compactness by providing a plurality of electrodes on a single surface of the semiconductor chip.
FIG. 5 shows a cross-section view of a transistor of the past which has a plurality of electrodes on a single surface of the semiconductor chip. In this semiconductor device of the past, as shown in FIG. 5, on one surface of a semiconductor chip 1 are provided a gate electrode (or base electrode) 41, a source electrode (or emitter electrode) 42, and a drain electrode (or collector electrode) 43.
In a transistor such as shown in FIG. 5, however, the following problem occurs.
In general, a transistor has characteristics such that, by applying a voltage to the gate electrode, the value of resistance between the drain electrode and the source electrode is reduced (this resistance value being referred to hereinafter as the on resistance). In this case, in order to cause a prescribed current to flow in the drain electrode, a voltage is applied to the drain electrode, this being smaller the smaller the on resistance is. While the power consumption of each transistor is not that large, because a large number of such transistors are provided in the circuit product, it is desirable that the power consumption of each transistor be made smaller. That is, because the power consumed to drive a transistor is smaller the smaller the on resistance is, it is desirable to make the on resistance of the transistor small.
The resistance value r of an electrode is generally determined as p=l/S (where p is the resistivity, l is the length of the electrode, and S is the cross-sectional area). In a semiconductor device of the past such as shown in FIG. 5, if the width W' of the drain electrode 43 is made larger, the resistance value r, which is the on resistance, becomes smaller. However, the drain electrode 43 is formed of a semiconductor substance formed by a diffusion process as described above, the only way to make the cross-sectional area, or the width W' of the drain electrode 43 large, is to make the semiconductor chip 1 larger. That is, in a semiconductor device of the past such as shown in FIG. 5, it is not possible to make the semiconductor chip itself small and obtain a sufficiently large on resistance. Thus, in a conventional semiconductor device, in the case in which the drain electrode and the source electrode are formed on one and the same surface and in which a drain electrode is formed in proximity to the gate electrode and source electrode, there was the problem of not being able to achieve a small enough overall size.
Accordingly, it is an object of the present invention to solve the above-noted problem in the prior art, by providing a compact, thin semiconductor device. It is a further object of the present invention to provide a method for manufacturing a semiconductor device featuring good productivity.